1. Field of the Invention
The present invention relates to a laying structure for linear elements, such as wires or pipes, located between two relatively rotating members, and more particularly, to a laying structure adapted to lay linear elements between relative rotation parts in a turning machine such as a robot or manipulator.
2. Description of the Related Art
A bundle of linear elements that are formed of wires and pipes, such as cables for supplying electricity and hoses through which a fluid such as air or water runs, is attached to and stretched between two members that can rotate relatively to each other. When the two members rotate relatively to each other, in this case, the bundle of linear elements is twisted, so that its durability lowers.
There are increasing demands for the enlargement of the range of operation of a robot and the improvement of the reliability of built-in cables of the robot, in particular. Accordingly, various proposals have been made to improve wiring and piping structures, such as cables, hoses, etc. in the relative rotation parts.
In the case of a robot wrist, in particular, a working unit such as a hand or welding gun is attached to the distal end of the wrist. Further, a plurality of linear elements, such as cables for supplying the working unit with electricity or hoses for running a fluid, such as air or water, are bundled and laid along an arm or wrist of the robot. Wrist elements of the robot wrist to which the working unit is attached frequently rotate and move relatively to a pedestal element, so that the durability of the linear elements is a critical problem.
There is a system to tackle this problem. According to this known system, the wrist elements are made hollow, and the central axis of the hollow is the center of relative rotation of the wrist elements. A bundle of linear elements, such as cables, is passed through the hollow structure. The bundle of linear elements is twined in the hollow structure as it is guided into the wrist elements so that the wrist element on the side of pedestal and the wrist element on the side of rotating part can rotate relative to each other within a given range.
As mentioned before, however, the hand, welding gun, or other working unit is attached to the rotating parts (wrist elements) on the distal end of the robot wrist, so that each rotating part may not be able to be formed in the shape of a pipe that has a through hole. In this case, the bundle of linear elements must be taken out through the side faces of the rotating parts.
FIG. 4 is a view illustrating relative rotation parts on the distal end of one such conventional robot wrist. A first wrist element 101 and a second wrist element 102 are formed having a hollow shape and a common central axis. The first wrist element 101 rotates relatively to the second wrist element 102 around the common central axis. The first wrist element 101 is formed having a flange portion on its distal end to which the hand, welding gun, or other working unit (not shown) can be attached. Thus, the distal end of the hollow first wrist element 101 is closed by the flange portion and is not pierced.
Accordingly, a bundle 10 of linear elements, which are formed of wires and pipes, such as cables for supplying electricity to the working unit on the flange portion of the first wrist element 101 and hoses through which air, water, or some other fluid runs, is led out through an opening 103 that is formed in the side face of the first wrist element 101.
The bundle 10 of linear elements passes through the respective hollow portions of the second and first wrist elements 102 and 101, bends in the shape of an L, and comes out through the opening 103 in the side face of the first wrist element 101. In the second wrist element 102, the bundle 10 is fixed by means of a fixing portion 104. In the first wrist element 101, the bundle 10 is fixed by means of a fixing portion 105 that is located near the opening 103.
When the first wrist element 101 rotates relatively to the second wrist element 102, therefore, the bundle 10 of linear elements also rotates together with the first wrist element 101, so that it is twisted in the direction of rotation of the element 101. If the first wrist element 101 repeatedly rotates in two opposite directions, it lowers the durability of the linear elements. If the number of linear elements that constitute each bundle 10 increases, the bundle 10 becomes so thick that it cannot be suddenly bent in the shape of an L with ease. Thus, the first wrist element 101 requires a wide space inside. If such a wide space is required in the robot wrist, however, the wrist must inevitably be large-sized, which is not structurally favorable.
Described in WO01/39933A1 is a method in which one bundle of linear elements is divided into a plurality of split bundles, and the split bundles are taken out in the direction of the radius of rotation of a first wrist element through an opening in its side face. According to this method, however, the split bundles inevitably gather and adhere to one another near the center of a hollow configuration that is located near the opening of the first wrist element. If the first wrist element rotates relatively to the second wrist element, therefore, a force to twist the bundles of linear elements is enhanced, and the split bundles strongly rub against one another, so that the durability of the bundles lowers.